JPH11145570A - Printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain electromagnetic interferences and unwanted electromagnetic waves caused by a signal wire connected between an analog and a digital circuit by a method, wherein analog/digital lands are provided corresponding directly to the analog circuit and the digital circuit, and a signal ground corresponding to both the circuits on a signal output side is made to extend. SOLUTION: An analog signal wire 2 transmits the output of an analog circuit, and an analog ground 4 is extended to enable a ground which corresponds to a signal wire to transmit signals to a digital circuit. The analog ground 4 corresponds directly to an analog circuit. A digital circuits and analog circuits are mixedly provided to a printed board 7, composed of conductor layers and a dielectric body 9, wherein the analog circuit and its output signal wire 2 correspond directly to an analog ground, the digital circuit corresponds directly to a digital ground 3, so that an electromagnetic interference and disused electromagnetic waves caused by a signal wire connected between both the circuits can be restrained. A digital signal wire which transmits signals to an analog circuit serves as a signal wire connected between both the circuits, and a digital ground 3 is extended.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board mounted in an electronic device, and more particularly to a printed circuit in which interference generated in an internal circuit of the electronic device and unnecessary electromagnetic waves generated from the electronic device are suppressed. It relates to a substrate.

[0002]

2. Description of the Related Art FIG. 7 shows a conventional printed wiring board disclosed in, for example, Japanese Patent Application Laid-Open No. 7-302959. In the figure, 101, 103 and 105 are digital circuit blocks,
102 and 104 are analog circuit blocks, 106 is a connection terminal, 110 is a chip component, 111, 112, 113,
114 and 115 are GND patterns, 111A to 111
C, 112A to 112C, 113A to 113E, 114
A to 114G, 115A to 115G are lands, 140
Is a substrate.

According to the above configuration, the GND pattern 111 in each of the circuit blocks 101 to 105 of the substrate 140 is provided.
115 are formed separately for each of the circuit blocks 101 to 105, and are connected to the corresponding connection terminals 106. Land portions 111A to 111C, 112A to 112C are included in the lines of the GND patterns 101 to 105, respectively.
C, 113A-113E, 114A-114G, 115
A to 115G are formed, and the land parts of the circuit blocks 101 to 105 can be connected to each other by the chip component 110 as appropriate. Therefore,
By further connecting the GND pattern of the circuit block with the chip component 110 so as to reduce the noise while actually measuring, the noise is reduced as a result, and the influence of voltage fluctuation between the circuit blocks is avoided.

When the ground is divided into a plurality of sections (circuits), it is often practiced to divide the ground into sections corresponding to analog circuits and digital circuits. As a second conventional example,
Japanese Patent Application Laid-Open No. Sho 63-170988 discloses that a ground for an analog circuit and a ground for a digital circuit are provided separately on two layers of a printed circuit board, and a signal line connecting both circuits is a through hole. Connects both sides of the printed circuit board to the analog side and the digital side on each side.

[0005]

The conventional printed wiring board is constructed as described above, and the ground (GND pattern) of each circuit block is naturally separated in the middle, so that the signal connecting each block is The structure is such that the ground corresponding to the line is interrupted on the way. In such a wiring structure, even if the ground is separated, no consideration is given to the signal lines connecting between the blocks or between the analog and digital circuits, thereby suppressing electromagnetic interference and unnecessary electromagnetic waves generated inside the electronic device. There was a problem that it was difficult.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a printed circuit board which suppresses electromagnetic interference and unnecessary electromagnetic waves caused by a signal line connecting an analog circuit and a digital circuit. And

[0007]

A printed circuit board according to the present invention is provided with an analog ground directly corresponding to an analog circuit and a digital ground directly corresponding to a digital circuit, and a signal line for connecting the analog circuit and the digital circuit. The signal line ground is provided by extending the ground corresponding to the circuit on the signal output side in both circuits.

Further, when the signal line ground includes an analog signal line for transmitting an analog circuit output and a digital signal line for transmitting a digital circuit output, the analog signal line ground extends the analog ground. The digital signal line ground is configured to extend the digital ground.

Further, the signal line ground has a width which is ten times or more the width of the corresponding signal line.

Further, a shield conductor is provided between the analog ground and the digital ground.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 In order to reduce noise on the signal line that connects digital and analog circuits, it is important to determine which side of the signal line transmits the output to the other input, that is, put importance on the output side, and suppress its influence. It is. Hereinafter, the configuration according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1A is a sectional view, and FIG.
(B) is a perspective view focusing only on the relationship between the ground and the signal line. In the figure, 2 is an analog signal line, 3 is digital ground, 4 is analog ground, 5 is digital I
C and 6 are analog ICs, 7 is a printed circuit board, and 9 is a dielectric. The ground corresponding to the signal line has a configuration in which the analog ground 4 is extended since the signal line 2 transmits the output of the analog circuit to the digital circuit in the example of FIG. The analog ground plane 4 directly corresponds to an analog circuit, and the digital ground 3 is not inserted between the analog ground plane 4 and the analog ground plane.

As shown in FIG. 1, a digital circuit and an analog circuit are mixed, and in a printed circuit board composed of each conductor layer and the dielectric 9, noise generated from each circuit is not simply inserted into another circuit. Therefore, it is not enough to separate the digital ground from the analog ground.
That is, the ground corresponding to the signal line connecting both circuits is interrupted on the way, so that electromagnetic interference and unnecessary electromagnetic waves due to this signal line are generated. According to the configuration shown in FIG. 1, the analog circuit and its output signal line directly correspond to the analog ground, and the digital circuit and the digital ground directly correspond to each other. Unwanted electromagnetic waves can be suppressed.

When the analog circuit portion and the digital circuit portion are interchanged and the signal line connecting the two circuits is a digital signal line for transmitting the output of the digital circuit to the analog circuit, the ground corresponding to the signal line is a digital ground. 3
May be extended. Also in this case, the digital circuit and the digital ground directly correspond to each other so that the analog ground does not enter between them.

Embodiment 2 FIG. An analog signal line for transmitting the output of an analog circuit to a digital circuit, and a digital signal line for transmitting the output of a reverse digital circuit to the analog circuit.
A description will be given of a noise reduction configuration when the type is a signal line. 2A and 2B are configuration diagrams of the substrate according to the present embodiment. FIG. 2A is a cross-sectional view, and FIG. 2B is a perspective view focusing on only ground and signal lines. In the figure, 1 is a digital signal line, 2 is an analog signal line, 3 is a digital ground, 4 is an analog ground, 5 is a digital IC, 6 is an analog IC, 7 is a printed circuit board, 8 is a through hole, 9
Is a dielectric.

In the configuration shown in FIG. 2, each signal line has a configuration in which the ground on the output side is extended, and the signal line and the corresponding ground are directly opposed to each other. Not even come in. As described above, the digital ground 3 and the analog ground 4 are respectively arranged and separated in different layers, and the signal line grounds immediately below the analog signal lines 2 and the digital signal lines 1 are made to coincide with the respective output-side grounds. Therefore, even when bidirectional signals are transmitted between circuits, electromagnetic interference and unnecessary electromagnetic waves can be suppressed.

Embodiment 3 In the above embodiment, the width of the signal line ground is not referred to, and FIGS. 1 and 2 show examples in which the entire width of the analog ground and the digital ground is extended as it is. In general, the characteristics are shown in FIG. 6 and the width of the ground corresponding to the signal line is 10 times or more the width of the signal line, as announced at the 1996 IEICE Communications Society Conference, B-257. Then, the characteristic impedance of the line is almost constant,
It is known to function as a microstrip line. A printed circuit board that can reduce the width of the signal line ground by using the above-described characteristics and divert the reduced area to another use will be described. FIG. 3 is a configuration perspective view focusing on the ground of the substrate in the present embodiment. In the figure, 2 is an analog signal line, 3 is a digital ground, 4 is an analog ground, 5 is a digital IC, and 6 is an analog IC.

In the configuration shown in FIG. 3, the digital IC 5 is a printed circuit board described in the first and second embodiments.
The width W of the analog ground or digital ground 3 extended to just below the analog signal line 2 or the digital signal line wired between the analog signal line 6 and the analog IC 6 is at least 10 times the width of the analog signal line 2 or the digital signal line. is there. According to the general theory described above, this width can sufficiently suppress the influence of interference, so that the occupied area of the arranged analog ground 4 or digital ground 3 can be reduced and the size can be reduced, or the area can be reduced for other uses. Diversion is possible.

Embodiment 4 The printed circuit board in each of the above embodiments has been described in the case where the analog circuit and the digital circuit are provided on the same surface side of the board. Here, a configuration in which the analog circuit and the digital circuit are separated on different surfaces on the substrate, that is, the front surface and the back surface, and further, the mutual interference between the two circuits is further described. FIG. 4 is a cross-sectional view illustrating the configuration of the substrate according to the present embodiment. In the figure, 2 is an analog signal line, 3 is a digital ground, 4 is an analog ground, 5 is a digital IC, 6 is an analog IC, 7 is a printed circuit board, 8 is a through hole, 9 is a dielectric, and 10 is a shield conductor. .

In the configuration shown in FIG. 5, a shield conductor 10 is further provided between digital ground 3 and analog ground 4 on printed circuit board 7 in the first to third embodiments.
Is provided. With this configuration, it is possible to further increase the effect of suppressing electromagnetic interference generated between digital and analog circuits and unnecessary electromagnetic waves generated from electronic devices.

The shield conductor 10 according to the present embodiment can be applied to the printed circuit board according to the above embodiment. FIG. 5 is a diagram showing an example thereof, which is applied to the substrate of the second embodiment. With this configuration, the same effect as that of the present embodiment can be obtained.

In each of the above embodiments, the case where the digital circuit and the analog circuit are separated from each other and connected by signal lines has been described. However, a circuit having a high sensitivity and a circuit having a low sensitivity and a circuit having a large amount of noise are provided. Also in the configuration in which a small number of circuits are separated and connected by a signal line, the same separation and the configuration in which the signal line extends the ground of the output side circuit can suppress electromagnetic interference and unnecessary electromagnetic waves. In addition, in the drawings shown in each embodiment, each part is arranged on the same cross section, but this is not necessarily required.

[0022]

As described above, the present invention has the effect of suppressing electromagnetic interference via signal lines connecting digital and analog circuits and unnecessary electromagnetic waves generated by electronic devices.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view and a ground perspective view of a printed circuit board according to Embodiment 1 of the present invention.

FIG. 2 is a cross-sectional view and a ground perspective view of a printed circuit board according to Embodiment 2 of the present invention.

FIG. 3 is a ground perspective view of a printed circuit board according to Embodiment 3 of the present invention.

FIG. 4 is a cross-sectional view of a printed circuit board according to Embodiment 4 of the present invention.

FIG. 5 is a sectional view of another printed circuit board according to the fourth embodiment.

FIG. 6 is a diagram illustrating a correspondence between a ground conductor width and a characteristic impedance.

FIG. 7 is a plan view showing an example of a conventional printed circuit board.

[Explanation of symbols]

1 digital signal line, 2 analog signal line, 3 digital ground, 4 analog ground, 5 digital I
C, 6 Analog IC, 7 Printed circuit board, 8 Through hole, 9 Dielectric, 10 Shield conductor.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koichi Segami 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric Co., Ltd. (72) Inventor Naoto Oka 2-3-2 Marunouchi, Chiyoda-ku, Tokyo (72) Inventor Mitsuhiko Kanda 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation

Claims (4)

[Claims] 1. A printed circuit board on which digital / analog circuits are mixed, wherein an analog ground directly corresponding to the analog circuit and a digital ground directly corresponding to the digital circuit are provided, and a signal line connecting the analog circuit and the digital circuit is provided. A printed circuit board, wherein a ground for a signal line corresponding to the signal line is provided, and the ground for the signal is a ground extended from a ground corresponding to a circuit on a signal output side in both circuits. 2. The signal line ground extends the analog ground when the signal line includes an analog signal line transmitting an analog circuit output and a digital signal line transmitting a digital circuit output. 2. The printed circuit board according to claim 1, wherein the digital signal line ground is configured to extend the digital ground. 3. The signal line ground according to claim 1, wherein the width of the signal line ground is at least ten times the width of the corresponding signal line.
2. The printed circuit board according to 2. 4. The printed circuit board according to claim 1, wherein a shield conductor is provided between the analog ground and the digital ground.